Petrogenesis,geochemistry And Tectonic Implication Of Guaizihu Composite Rock Body In Alxa Of Inner Mongolia

IIIn the region of Guaizihu in Alxa Inner Mongolia had experienced a complex geological evolution, with many multi-phase and multi-stage granities in Late Hercynian being developed. We renewed the disintergration of Guaizihu composite rock body in the paper which based on the results of zircon U-Pb geochronology and regional geology survey data. According to research petrological and geochemical characteristics of the Guaizihu composite rock body and intergrate the results of project team, the paper foucused on thier formation time, petrogenesis, origin of petrologic material, tectonic setting and geological significance.According to the zircon U-Pb geochronology of the composite rock body, we have got three groups of age. The age of porphyaceous granodioritic spaned 370-390Ma; fine-grained structure granodioritic concentrated in the age of 315Ma; the age of porphyaceous biotite granite spaned 260-270 Ma. Based on the results of geochronology, the Guaizihu composite rock body can be broken up into three ages to dicuss and research, which are respectively Devonian, Carboniferous and Permian granities. Devonian rock association which are: gray porphyritic granodiorite and porphyritic red light meat adamellite; Carboniferous rock compositions are: gabbro-diabase, gray fine-grained granodiorite K-feldspar granite and red meat moyites; Permian granite is composed of gray porphyritic biotite granite.Devonian granities are mainly composed of porphyaceous granodioritic and porphyaceous adamellite. They are characterized by occurrence of museovitein and garnet mineral assemblage. And its geochemistry imply the characteristics of high-alumina, low magnesium and titanium, peraluminous and high potassium calc-alkaline. And they are identified as S-type granite, which is derived from melting of crust, mostly are greywacke. The trace element is characterized evidently by neg-ative anomaly of P,Sr, Ba, Nb, etc and positive anomaly of U,Zr,Hf, etc,which imply plagioclase of source area experienced fractional crystallization. Carboniferous and Permian granities are mainly composed of gabbro-diabase, fine-grained structure granodioritic, moyite and porphyaceous biotite granite. The two rock body had the similar characteristics. They belong to metaluminous-weak peraluminous calc-alkaline series I-type granite. The characteristics of trace element are similar to Devonian granities, but the content are lower. According to research we can know that Devonian granities are formed in the extrusion-stretching transformation post-collision environment. The Devonian intrusions are the first time to find in the area, which is the best response to the close of north Mongolia ocean and crustal collision.It implys the close time of north ocean is earlier than 370-390 Ma. Carboniferous and Permian granities are formed in volcanic arc environment by regional structure research,which are mainly formed in crustal extension process. At the same time it implys the close of Engel Wusu ocean earlier than 260-270 Ma.